Heat exchangers, such as condensers in steam power plants, are often comprised of a set of tubes having cold water passing through the interior thereof and steam passing over the exterior thereof. The cold water directed through the interior of the tubes often carries with it a variety of biological substances which may adhere to and grow on the interior surfaces of the tubes. This biological fouling of the tubes reduces the rate of heat transfer in the condenser. This reduces the efficiency of the power plant, requiring that the power plant be taken offline periodically for manual cleansing of the tubes.
Biofouling has been effectively controlled by injecting chlorine, bromine, hot water, or other biocides into the cold water stream. The condensers in steam power plants usually discharge their cooling water directly into the environment (e.g. river, lake or ocean). Often, the treatment fluids added to the cooling water are hazardous to the environment when delivered in the high concentrations necessary to be effective.
Condenser tubes incur leaks on occasion which allows the cooling water to contaminate the steam passing over the tubes. Since such contamination can cause substantial corrosion problems and increased maintenance requirements in other parts of the power plant, efforts are made to detect and fix tube leaks as quickly as possible. One leak detection strategy requires injection of sulfur hexafluoride (SF.sub.6) or some other leak detection fluid, into tubes of the condenser.
Attempts have been made to deliver high concentrations of treatment fluid (i.e. biofouling control or leak detection agent) to only a fraction of the total number of tubes initially and then to deliver the treatment fluid sequentially to other groups of tubes, so that eventually all tubes are treated before the targeting cycle begins again. An advantage of this targeted treatment approach is that the targeted tubes receive the high concentration of treatment fluid needed for effective biofouling control (or tube leak detection) while the discharge is diluted in the outlet waterbox with the untreated water from the non-targeted tubes. Thus, the cooling water effluent leaving the plant does not pose an environmental threat.
One known fluid delivery system of this nature uses fixed nozzles which are activated sequentially to direct relatively high doses of treatment fluid to selected areas of an inlet tubesheet of the condenser. The fixed nozzles are mounted on the rear of the inlet waterbox of the condenser and deliver high velocity jets. While this fixed nozzle design is effective, it has a number of disadvantages. The fixed nozzle design requires relatively large nozzles (4 to 6 inches in diameter) and high treatment fluid flow rates (2,000 to 3,000 gallons per minute) to restrict the treatment fluid to the targeted area and overcome the dispersion tendency caused by waterbox turbulence. This requires a large external distribution piping and valve system. Another disadvantage of the fixed nozzle design is that the nozzles are located on the rear of the waterbox, a significant distance away from the tubesheet. This results in uneven distribution of treatment fluid to the tubes and requires that an excessive amount of treatment fluid be delivered to ensure adequate concentrations at all of the targeted tubes.
Another attempt that involves directing the treatment fluid to only a portion of the tubes at a time is described in U.S. Pat. No. 4,531,571 to Moss. Moss teaches the use of a fluid delivery system which includes a moveable manifold directly adjacent to the tubesheet. The manifold is moved to deliver fluid to different tubes by being rotated about a pivot. The device taught by Moss is inherently susceptible to jamming of the moveable manifold thereby disabling the system. A breakdown such as this requires some down time of that condenser to allow access to the interior of the waterbox.